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Table 2 Adjusted mean mammographic density measures according to reproductive and hormonal exposures among premenopausal women

From: Predictors of mammographic density among women with a strong family history of breast cancer

   Premenopausal women (n = 97)
  Percent Density (%)   Dense Area (cm2)   Non-Dense Area (cm2)
n Mean1 PD 95% CI1 P 1 n Mean1 DA 95% CI1 P 1 n Mean1 NDA 95% CI1 P 1
Age at menarche
 <13 years 32 29.9 20.0-41.8   28 31.1 17.2-49.2   28 80.1 50.4-116.7  
 ≥13 years 65 28.2 19.6-38.3 0.69 60 35.3 22.5-51.1 0.49 60 98.2 69.8-131.6 0.16
Parity
 Nulliparous 26 32.5 21.5-45.8   23 37.1 21.4-57.0   23 93.6 60.5-133.8  
 Parous 71 28.1 19.7-38.1 0.33 65 33.8 21.3-49.2 0.61 65 93.9 66.1-126.6 0.98
Total live births2
 1 21 41.6 27.2-59.0 ref 19 50.1 28.0-78.6 ref 19 71.7 39.0-114.3 ref
 2 35 28.8 17.8-42.3 0.04 32 32.9 17.2-53.7 0.06 32 84.7 52.2-125.0 0.40
 ≥3 15 29.1 15.3-47.3 0.12 14 33.0 13.7-60.8 0.14 14 82.5 42.6-135.3 0.58
Breastfeeding2
 Never 4 34.9 13.2-67.0   4 44.1 13.7-91.8   4 77.9 26.9-155.3  
 Ever 66 31.7 20.7-45.1 0.79 61 36.0 19.8-56.9 0.64 61 81.5 50.7-119.6 0.90
Breastfeeding duration2
 <11 months 30 32.7 18.7-50.5   31 41.9 21.2-69.6   31 76.5 41.4-122.4  
 ≥11 months 40 31.7 20.6-45.2 0.87 34 34.9 18.9-55.8 0.43 34 82.8 51.3-121.8 0.69
OC use
 Never 10 29.6 17.5-44.9   9 33.2 15.8-57.1   9 72.4 38.4-117.2  
 Ever 87 28.5 19.9-38.7 0.87 79 34.5 21.9-50.0 0.89 79 97.3 69.1-130.3 0.18
Duration of OC use
 <9 years 40 37.4 25.2-52.0   37 41.5 24.6-62.8   37 79.9 50.0-116.8  
 ≥9 years 47 33.0 22.1-46.0 0.32 42 35.9 20.4-55.9 0.39 42 86.1 54.9-124.2 0.60
  1. 1Adjusted least-square means, 95% confidence intervals, and P-values are from analyses using square root-transformed mammographic density measures. The adjusted least-square means and 95% confidence intervals were back-transformed
  2. 2Among parous women only
  3. All models were adjusted for age (continuous) and BMI (continuous) at the time of mammogram, parity (continuous), and mammogram modality (digital image, film scanned by study team, film scanned by imaging centre). The parity (total live births) and breastfeeding models were additionally adjusted for age at first birth (continuous). OC, oral contraceptives